Double notes: thirds and sixths

Scales in thirds and sixths are among the most dreaded challenges: Chopin devoted two études to them (Op. 25 No. 6 in thirds, Op. 25 No. 8 in sixths), and they are everywhere in Liszt, Brahms and Ravel. They require legato in at least one voice, perfect simultaneity and great suppleness.

The fingering principle

In thirds, the right hand alternates three finger pairs: 1-3, 2-4, 3-5. On reaching 3-5, the hand must reposition: the thumb passes under the 3rd (for the lower voice) while the upper voice connects from 5 to 4 or 3. It is impossible to play everything legato: you choose the upper voice (the melody) for legato and accept slight breaks in the lower voice, which pedal or phrasing conceal.

M:4/4
L:1/8
Q:1/4=60
K:C
[CE][DF][EG][FA] [GB][Ac][Bd][ce] | [df][ce][Bd][Ac] [GB][FA][EG][DF] | [CE]8 |]

One common fingering for this scale in thirds (right hand, ascending): C-E 1-3, D-F 2-4, E-G 3-5, F-A 1-3, G-B 2-4, A-C 3-5, B-D 1-3 (or 1-4), C-E 2-4… Several systems exist (Cortot, Godowsky, Czerny): choose one and stick to it.

Sixths

They require a wider stretch: the lower voice is often played by the thumb (sometimes sliding from a black key to a white one), the upper voice by 4 and 5 alternately (with 3 on black keys for large hands). The upper legato relies on a very supple hand that "rolls" from one sixth to the next.

Practice plan

1. Upper voice alone, with the thirds fingering, perfectly legato.
2. Lower voice alone, with its fingering.
3. Both voices together, very slowly, pp, checking simultaneity.
4. In groups of three thirds (matching the 1-3/2-4/3-5 positions), stopping on the first of each group.
5. Dotted and reversed rhythms, as for scales (see practising scales).